The present invention relates to systems for measuring blood pressure. In particular, the invention relates to a method and apparatus for indicating and maintaining a blood pressure sensing device over an underlying artery.
Blood pressure may be measured either invasively or non-invasively. Invasively measuring blood pressure using an arterial line (A-LINE) involves insertion of a needle into the artery. A transducer connected to the needle by a fluid column is used to determine exact arterial pressure from the inserted needle.
Alternatively, blood pressure may be measured non-invasively. Non-invasive measurement of blood pressure typically requires that an external blood pressure sensing device having a sensing surface be positioned over and above an artery. Typically, a physician will palpate the artery and mark a location above the artery. The sensing surface of the sensing device is then centered over this mark.
Although seemingly simple, accurately locating the external blood pressure sensing device over the underlying artery may be extremely difficult. Because the sensing device is often opaque and has a surface area much larger than the mark indicating the location of the artery, a physician cannot view the mark or the underlying artery while positioning the sensing device. As a result, centering the sensing device over the mark or over the underlying artery is extremely difficult and time consuming.
This problem is further magnified because the sensing device is frequently removed or becomes dislodged from its original location and must be repeatably repositioned over the artery. For example, during a typical hospital procedure, the patient may be moved from pre-operative care to surgery, to recovery, to intensive care and then to a less acute care step down area of the hospital. At each location, a physician must relocate and once again center the sensing device over the mark indicating the underlying artery. In instances where the mark has worn away, the physician must once again palpate the artery, mark the location and center the sensor over the mark. As a result, the necessity of repeatingly centering the sensor over the mark or identifying the location of the artery is time consuming and expensive.
Once the sensor is centered over the mark and above the underlined artery, patient movement frequently moves and dislodges the sensor from its original position. Consequently, the sensor must once again be recentered over the mark and above the underlying artery. Although accidental movement of the sensor from its original location may be minimized by the physician tightening a strap or other structure that holds the sensing device about the wrist, tightening of the strap or belt may cut off or reduce blood flow. This reduction of blood flow may cause swelling of the patient's hand or other related anatomy.